Signal interpretation of partial discharges in three-phase medium voltage cable systems measured on-line

Measuring partial discharges online in three-phase power cable systems has a number of implications on the signal interpretation as compared to offline measurements with only one phase energized. The induced currents and charges in the phase conductors and earth screen upon a PD not only depend on the discharge site, but also become phase angle dependent. Furthermore, simulations show that the PD distribution itself varies with the amount of eccentricity of the rotating field and may differ from the offline distributions obtained with a linear field. Finally, the PD propagation in a multi-conductor cable also alters the signals measured at the cable terminals. In this paper, these implications are studied by means of computer simulation.